This invention relates to the mechanism of a recording and reproducing apparatus and more particularly to a mechanism suitable for reducing the size and weight of the apparatus and for simplifying the apparatus structure.
Conventional recording and reproducing apparatuses employ the following mechanisms as detailed in (1), (2) and (3) below.
(1) A cam mechanism is a mechanism for changing the direction and amount of motion and is used in a variety of recording and reproducing apparatuses. In a video tape recorder, for example, various kinds of cam mechanisms are employed to perform operations such as (a) application and release of a brake, (b) engagement and disengagement of a pinch roller, and (c) operation of a tension control arm. These operations are required by a mode switching between such modes as (1) fast feeding/fast rewinding, (2) stopping, (3) recording/replaying and (4) reverse replaying.
One such example is a cam disclosed in the Japanese Patent Application Laid-Open No. 58-60450 in which a cam member has a guiding portion or a slider extending in the direction of the cam movement.
A mode selection mechanism using a ring-shaped cam member is disclosed by the Japanese Patent Application Laid-Open No. 61-242364, the corresponding U.S. Pat. No. 4,748,521 and the corresponding European Patent Application Publication No. 0 198 512.
(2) Recording and reproducing apparatuses such as video tape recorders use a tape loading mechanism that drives and guides a pair of tape guides around a rotating drum to wind a magnetic tape (or simply referred to as tape) contained in a tape cassette around the drum a specified angle. One such mechanism is described in the Japanese Patent Application Laid-Open No. 58-218066. This mechanism consists of two moving rings (first and second rings) that move around the rotating drum to drive a pair of tape guides (first and second tape guides), and a drive ring to drive the first and second moving rings, these three rings being concentrically and rotatably stacked one upon the other. A similar mechanisms is also known which employs arc sliders instead of rings In such tape loading mechanisms, the rotating ring or arc slider is held and supported, on its outer or inner circumference, by gears that engage with a gear formed on the ring or arc slider and by a roller.
(3) Recording and reproducing apparatus such as video tape recorders have a tape loading mechanism which draws out the tape from a tape cassette by means of a tape guide moving along a guide path and winds the tape around the rotating drum a specified angle. Guiding the tape guide along a guide path is accomplished by a mechanism described in the Japanese Patent Application Laid-Open No. 57-133558, which consists of a T-shaped rail (guiding member) and a tape guide with a C-shaped clamp portion that clamps the rail. The tape guide is required to move along a complicated path performing a combination of such motions as straight line advance, turning and diagonal movement while avoiding interference with the tape guide and associated parts (e.g., stationary head, height restriction guide and rotating drum) mounted on a chassis. Conventional apparatuses provide a large clearance between the rail and the tape guide to allow for complicated movement of the tape guide and the play resulting from the large clearance is offset by a spring.
The above three conventional techniques (1), (2) and (3) have the following problems (1), (2) and (3), respectively.
(1) In the cam mechanism of the above technique (1), when a plurality of mechanism elements have different patterns of motion, it is necessary to provide cams each dedicated to each element. To meet this requirement, the following three methods have commonly been practiced.
(a) The cam member is elongated in a longitudinal direction to connect cams in series. PA1 (b) The width of the cam member is increased and cams are provided on each side of the cam member; or a plurality of cam patterns are arranged parallelly in the direction of width. PA1 (c) The thickness of the cam member is increased and a plurality of cam patterns are arranged in layers in the direction of thickness.
In any of the above methods, the problem is that the cam member necessarily becomes large, which in turn increases the size of the cam mechanism and therefore the apparatus as a whole.
(2) As to the conventional technique of item (2), no consideration is taken regarding the play of arc slider and the engagement of gear during the process of holding the arc slider. Let us consider the case of an arc slider with a gear formed along the outer circumference. To hold and support the arc slider requires at least three members--a first gear for driving the arc slider, a second gear for supporting the outer circumference of the arc slider, and a roller located between the two gears for receiving the inner circumference of the arc slider. However, as these members rotate through large angles, there are states where the arc slider and gears are not in mesh. When in this condition it is attempted to bring the arc slider and the gears into mesh, the arc slider may fail to come into smooth meshing engagement with the gears because of the deflection of the slider and because of the plays and backlash between the gear supporting the outer circumference of the slider and the gear portion on the slider, resulting in the arc slider halting during operation. To solve this problem, it is necessary to use three or more gears and rollers and also provide a special mechanism or device to eliminate improper engagement of gears, which in turn increases the number of parts used and therefore the space to accommodate them.
(3) The conventional technique of item (3) requires a spring to offset the clearance between the rail and the tape guide. This gives rise to problems such as difficulty in forming the tape guide in a desired shape and in reducing the size of the mechanism as a whole It also increases the number of parts. Moreover, since the tape guide is simply held on the rail by a spring, the posture of the tape guide is difficult to maintain during loading, raising the possibility of the tape being damaged.